The present invention relates to a sensor device for mounting at or on a shaft of an electric machine, having a detection device for detecting a bearing current of the electric machine.
Bearing currents frequently occur in converter-fed electric machines. They very quickly cause damage to the ball or roller bearing, resulting in drive failure. To detect bearing currents, permanently mounted sensor systems are therefore used. These are designed to continuously monitor the drive. As the bearing currents cannot be measured directly during actual operation of equipment, the proposed bearing current sensors detect the occurrence of bearing currents by measuring the electric shaft potential of the machine. For this purpose either a sliding contact (brush) or contactless connection (e.g. by means of capacitive coupling) is used. The advantage of a contactless connection is that there no wear, i.e. no maintenance is required.
Such a sensor system requires an energy supply for operation. Mounting a bearing current sensor on a motor shaft or a shaft bearing therefore poses the question of how the sensor can be supplied with energy.
Supplying energy from the load circuit (power supply of the motor) is only possible with great complexity because of the high voltages and powers often present. Another possibility for generating energy is to use electromagnetic fields in the immediate vicinity of the electric machine. The latter are becoming ever fewer as leakage is optimized, and are therefore becoming more difficult to use.
At present, batteries or installed power supply units are normally used to supply energy to motor-associated sensors. These solutions result in increased maintenance requirements or additional installation costs.
All in all, a sensor system for detecting the bearing current is typically composed of the following components: coupling, sensor, evaluation unit, power supply or battery. These are generally implemented by a plurality of separate constructional units or devices.
The object of the present invention is therefore to reduce the complexity for detecting bearing currents in electric machines.